How much would a cathode follower drift ?

00940 · 24th November 2010, 12:09 PM

In the following schematic, what kind voltage of drift should I expect at the output over time ?

The output would go into an output transformer that can't stand more than a few mA of DC current and I wonder if I should implement a DC servo (probably a copy of SY's Heretical).

Thanks

DF96 · 24th November 2010, 12:42 PM

It will drift a huge amount. This is because for DC purposes the CF is not a CF at all but common-cathode with cathode bias. Without a DC servo there is little chance of the output ever being near 0V.

A DC CF would be better, but still not good enough if you want accuracy to mA levels.

00940 · 24th November 2010, 03:23 PM

Thanks.

A servo is no big deal after all... it avoids the nightmare of matching a parafeed cap to the output xformer for best frequency response.

24th November 2010, 03:23 PM	#3
00940 diyAudio Member Join Date: Sep 2003 Location: Paris	Thanks. A servo is no big deal after all... it avoids the nightmare of matching a parafeed cap to the output xformer for best frequency response. __________________ Ben.

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24th November 2010, 12:42 PM	#2
DF96 diyAudio Member Join Date: May 2007	It will drift a huge amount. This is because for DC purposes the CF is not a CF at all but common-cathode with cathode bias. Without a DC servo there is little chance of the output ever being near 0V. A DC CF would be better, but still not good enough if you want accuracy to mA levels.

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